So i've got a 12 ga mossberg 500 mariner with knox stock. I finally shot it over the weekend for the first time. I had a few times where the fore-end wouldn't slide down to eject the shell. The little slide lock behind the trigger guard was pushed in, and i couldn't do anything to get it open. I had to really manhandle the fore-end and that got the extractor to eject the shell. Also, another time i had a shell get caught in the ejection port.(stovepipe) My question is..do you think i'm just not pulling the fore-end down with as much force as i need to? Or am i using shotgun loads that are too much for my shotgun? Is there a limit to what can be shot out of my sweet mariner? I was shooting buckshot out of it, and i was shooting some rifled slugs as well. I think the slugs were at 1600 fps. thanks fellas.